LeetCode -- Reorder List

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/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void ReorderList(ListNode head) 
    {
        if(head == null || head.next == null || head.next.next == null){
    		return;
    	}
    	
    	var p = head;
    	var q = head;
    	while(q.next.next != null){
    		while(p.next.next != null){
    			p = p.next;
    		}
    		
    		// point head to last
    		var t = q.next;
    		q.next = p.next;
    		// point last to 2nd and set the second last to null
    		p.next.next = t;
    		
    		// point 2nd last to null
    		p.next = null;
    
    		// reset p and q
    		p = t;
    		q = t;
    		if(q.next == null){
    			break;
    		}
    	}
    }
}

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     public int val;
 *     public ListNode next;
 *     public ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public void ReorderList(ListNode head) 
    {
        if(head == null || head.next == null || head.next.next == null){
    		return;
    	}
    	
    	var slow = head;
    	var fast = head;
    	while(fast.next != null && fast.next.next != null)
    	{
    		slow = slow.next;
    		fast = fast.next.next;
    	}
    	
    	var mid = slow.next;
    	var last = mid;
    	ListNode pre = null;
    	while(last != null){
    		ListNode next = last.next;
    		last.next = pre;
    		pre = last;
    		last = next;
    	}
    	slow.next = null;
    	
    	while(head != null && pre != null)
    	{
    		var next1 = head.next;
    		head.next = pre;
    		pre = pre.next;
    		head.next.next = next1;
    		head = next1;
    	}
    }
}

LeetCode -- Reorder List

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原文地址：http://blog.csdn.net/lan_liang/article/details/49962425